1. Field of the Invention
This invention relates to the field of power supplies, and particularly to cooling a power supply with a fan.
2. Description of the Related Art
The internal components of a power supply can generate a great deal of heat. Without appropriate cooling, these components can overheat and fail. Fans are commonly used in power supplies and computers to provide a relatively cheap cooling solution. In combination with additional elements, such as heat sinks for components that run particularly hot, most cooling problems can be solved with a fan.
However, it is generally not enough to simply place a fan in a power supply and run the fan at a constant speed. Running the fan at a constant high speed wears the components of the fan unnecessarily, wastes energy, and creates unnecessary noise. However, running the fan at a constant low speed prevents the fan from properly cooling the power supply when the power supply is running particularly hot. As a result, fans have control mechanisms to adjust the speed of the fan up and down based on the requirements of the power supply.
This requires, of course, a determination of how fast to run the fan at a particular moment. Prior art solutions often base fan speed on the temperature of the power supply. This, however, poses a host of problems. First, the ambient temperature of the power supply lags behind the temperature of the components themselves; as a result, the fan may not speed up in time. An additional problem is the placement of the devices that measure temperature in the power supply. The devices will naturally be sensitive to the temperature of components located nearby, but may not detect a rise in temperature of components located farther away. As a result, a component may fail since it does not contribute enough to the ambient temperature to register a change in fan speed.
Those in the art have tried to compensate for this shortcoming by making additional measurements. However, it can be difficult to tie additional parameters to temperature; for example, a very efficient power supply may deliver a high output power or output current without the components getting very hot. Prior art solutions force the fan to run unnecessarily fast in this case. In other situations, such as with a phase shift regulated power supply, the full bridge MOSFETs run very hot even though the output power and current are very low. In this case, the fan may fail to detect the heat quickly enough and the power supply can fail.